Garbage disposals are simple machines–basically a motor and a flywheel with impeller arms that spin and shred whatever they touch. Sometimes, though, the machine can jam on a bottle top or other debris, or trip a circuit breaker when it’s overloaded. If that happens, you just need to take a quick step or two to repair it.
Turn the garbage disposal on and off quickly and check to see if it has power. If it hums, the power is on but the impeller is jammed. Move on to step 3. If it doesn't hum, it may have overheated and tripped a circuit breaker. Move on to step 2.